Metal Skeleton Research Articles

Solution and solid-state nuclear magnetic resonance studies on interstitial atoms within transition-metal carbonyl clusters

The bonding of the interstitial atoms (C and N) within the metal skeleton in a series of transition-metal carbonyl clusters has been investigated by NMR studies of the shielding anisotropy and asymmetry in solution and in the solid state. Observed shielding anisotropies suggest that the hybridisation of the interstitial atom is dependent on the metal geometry and tends towards sp in an octahedral, sp2 in a trigonal-prismatic and sp3 in a square-antiprismatic metal skeleton.

Reactivity patterns of the unsaturated tetrahedral cluster [Re4(µ3-H)4(CO)12]. Easy addition of four MeCN molecules and ‘ionic’ or ‘neutral’ fragmentation pathways of the spiked-triangle intermediate [Re4(µ-H)4(CO)12(NCMe)4

The unsaturated (56 valence electrons, v.e.s) tetrahedral cluster [Re4(µ3-H)4(CO)12]1 readily added four acetonitrile molecules, affording two isomers 2a and 2b of the 64 v.e.s [Re4(µ-H)4(CO)12-(NCMe)4] derivative, containing a spiked-triangle metallic skeleton. These isomers at room temperature rapidly underwent an ionic fragmentation to the known unsaturated triangular cluster anion [Re3(µ-H)4(CO)9(NCMe)]– and to the cation [Re(CO)3(NCMe)3]+. The rate of decomposition significantly increased at low [MeCN] concentration. Treatment of compounds 2a and 2b with the π-acidic ligand CO, in the absence of free acetonitrile, gave only neutral products. Monitoring by NMR spectroscopy has revealed the rapid stepwise substitution of the nitrile ligands, accompanied by fragmentation to the known saturated triangular clusters [Re3(µ-H)3(CO)12 –n(NCMe)n](n= 1–3) and to the mononuclear complexes [ReH(CO)5 –n(NCMe)n](n= 0 or 1). The novel, unstable, mononuclear hydride [ReH(CO)4(NCMe)] has been obtained by treatment of [ReH(CO)5] with Me3NO in acetonitrile and by reaction of [ReH2(CO)4]– with CF3SO3H, in acetonitrile. In the presence of free acetonitrile, compounds 2a and 2b reacted with CO more slowly and gave both anionic and neutral triangular clusters.

Syntheses and molecular structures of two boride cluster anions: octahedral [Rh2Ru4(CO)16B]? and double-prismatic [Rh3Ru6(CO)23B2

The compounds [N(PPh3)2][Rh2Ru4(CO)16B]1 and [N(PPh3)2][Rh3Ru6(CO)23B2]3 were isolated after treating [N(PPh3)2][Ru3(CO)9BH4] with [{Rh(CO)2Cl}2] for 1 h. The neutral cluster [Rh2Ru4H(CO)16B]2 was also isolated. The crystal structure of 1 has been determined: monoclinic, space group P21/n, a= 16.370(5), b= 10.330(3), c= 33.532(9)A, β= 96.33(2)°, Z= 4. The core of 1 is octahedral with the two rhodium atoms in a trans arrangement; the boron atom is sited at the centre of the octahedron. The crystal structure of 3 has also been determined: triclinic, space group P, a= 10.666(2), b= 17.540(4), c= 18.658(3)A, α= 91.06(2), β= 104.15(2), γ= 92.54(2)°, Z= 2. The cluster core consists of two, face-sharing prisms with one square face capped by a rhodium carbonyl fragment; each prismatic cavity contains a boron atom and B–B separation is 1.80(2)A. The structure of cluster 3 is novel both as far as the environment of the boron atoms and the geometry of the metal skeleton are concerned but it is related to a series of previously characterised carbido clusters.

Synthesis and solid-state structure of [Pd6Ru6(CO)24]2–. Electrochemistry and13C nuclear magnetic resonance spectra of [Fe6Pd6H(CO)24]3–and [Pd6Ru6(CO)24]2–

The cluster [Pd6Ru6(CO)24]2– was obtained in good yield from the reaction of [Ru3H(CO)11]– with [Pd(NCPh)2Cl2]. The salt [NEt4]2[Pd6Ru6(CO)24] crystallized in the triclinic space group P(no. 2) with a= 11.514(5), b= 11.602(5), c= 11.933(5)A, α= 73.01 (3), β= 78.25(3), γ= 65.26(4)°, Z= 1. Data were collected at room temperature, giving 5968 unique reflections. The structure was solved by direct methods. The final discrepancy indices were R= 0.024 and R′= 0.026 for 4129 independent reflections with I > 3σ(I). The metal skeleton consists of a trigonally distorted octahedron of palladium atoms, capped by six ruthenium atoms with twelve terminal, six edge- and six face-bridging carbonyl ligands. This ruthenium–palladium cluster adopts the same metallic polyhedron as [Fe6Pd6H(CO)24]3– but possesses two valence electrons less. The solution 13C NMR spectra of both anions are in agreement with the solid-state structures and electrochemical analysis shows that they produce labile congeners: [Pd6Ru6(CO)24]2– undergoes a one-electron oxidation with formation of the relatively stable monoanion; [Fe6Pd6H(CO)24]3– can be oxidized and reduced, to give corresponding anions with charges of 2– to 5–.

Chemistry of iridium carbonyl cluster complexes. Synthesis and x-ray crystal structure of [PPh4]2[Ir12(.mu.-CO)5(CO)19], containing an unprecedented metal skeleton

The new dodecanuclear carbonyl cluster [Ir 12 (CO) 24 ] 2- can be prepared in good yields by thermal treatment of [Ir 6 (CO) 15 {Cu(NCMe)}] - in refluxing tetrahydrofuran: the anion has been characterized as the tetraphenylphosphonium salt by a crystallographic study. [PPh 4 ] 2 [Ir 12 (CO) 24 ] crystallizes in the triclinic space group P1 with cell constants a=14.614(5) A, b=25.435(6) A, c=11.977(5) A, α=90.30(3) o , β=112.94(3) o , γ=104.33(2) o , V=3946(5) A 3 , and Z=2

Synthesis and Single Crystal Structure Determination of Bis(carbido)bis(μ-diphenylphosphido)heptadecacarbonyloctaruthenium-Dichloromethane (1/1), Ru8(μ6-C)(μ5-C)(μ-PPh2)2(CO)17.CH2Cl2

The synthesis and room-temperature single-crystal X-ray structure determination of the title compound are recorded. Crystals are monoclinic, P 21/c, a 14.43(2), b 18.39(1), c 23.64(3) Ǻ, β 123.16(7)°, Z = 4, isostructural with the recently described Fe3Ru5 analogue; R was 0.048 for 6892 'observed' data [I > 3σ(I)]. The cluster is one of the few containing separated carbide ligands within a polyhedral metal skeleton, consisting of an Ru5C square pyramid and an Ru6C octahedron sharing a triangular face, with two PPh2 groups bridging opposite Ru-Ru vectors in each polyhedron.

Synthesis of tetranuclear heterometallic cluster complexes via condensation of triosmium alkyne complexes OS 3(CO) 10(C 2R 2), R = Tol and Me, and mononuclear tungsten acetylide complexes LW(CO) 3)CCR′, L  Cp and Cp★, R′= Ph and tBu

Synthesis of tetranuclear heterometallic cluster complexes via condensation of triosmium alkyne complexes OS 3(CO) 10(C 2R 2), R = Tol and Me, and mononuclear tungsten acetylide complexes LW(CO) 3)CCR′, L  Cp and Cp★, R′= Ph and tBu

The application of transmission electron microscopy to the study of high nuclearity carbonyl clusters (HNCC's)

The properties of a variety of HNCC's supported on holey carbon films have been investigated by transmission and analytical electron microscopy; a review of how these techniques can be used to study these crystallographically well-characterized clusters is also presented. Images of the metallic skeleton corresponding to a single cluster unit have been observed for [Ni38Pt6(CO)48H]5−, [Ni34C4(CO)38H]5−, [Pt38(CO)44Hx]2−, [Rh17S2(CO)32]3−, [Ni12Sn(CO)22]2−, and [Ni22Ge(CO)22]2−, and analytical data at low electron beam intensities are consistent with their crystallographically established structures. At increasing current densities, agglomeration into larger particles occurs and these larger particles (2–5 nm) gradually lose the chemical identity of the precursor. Ultimately at current densities of the order of 107 A/m2 metal segregation and/or metal alloy particles having close-packed crystal structures are formed together with graphitic carbon from decomposition of the CO ligands. Possible mechanisms for this beam damage are discussed. There is evidence of cluster/substrate interaction resulting in increased stability compared to that observed in solution and in the normal crystalline state.

Giant Palladium Clusters: Synthesis and Characterization

ABSTRACTA series of palladium clusters containing from 4 to some hundred Pd atoms in the metal skeleton was prepared and characterized with structural data as well as by chemical properties including catalytic activity. An agreement between X-ray and EXAFS data was obtained for single-crystal low-molecular clusters. Giant clusters approximated as Pd56L60(OCOCH3)180 (L=Phen, Bipy) and Pd561Phen60O60X60 (X = PF6, CIO4, SO4, BF4, CF3COO)were characterized with TEM, SAXS, EXAFS, NMR, and magnetic susceptibility data. The clusters consisting of close-packed metal core and L, X ligands at its periphery could be considered as a bridge between low-molecular clusters and the particles of colloidal metals.

Synthesis and structure of the planar metal carbonyl Os5(CO)18

The new binary metal carbonyl Os5(CO)18 has been prepared by pyrolysis of Os5(CO)19 and shown by X-ray crystallography to have a planar metal skeleton.

Synthesis and characterization of heterometallic carbonyl cluster anions

The chemistry of rhodium carbonyl cluster anions is a guide-line for the rational synthesis of those mixed-metal clusters which contain rhodium associated with a metal of group VIII. The work presented here concerns reductions of neutral carbonylic substrata and redox condensations, performed under a carbon monoxide atmosphere which limits the nuclearity to 6–7 metal atoms and induces metal redistribution amongst the various species. The reduction degree of a species ( i.e. the ratio anionic charge/metal atoms) is a function of the reducing strength (or basicity) of the medium and can be chosen with some accuracy, while the internal Rh:M ratio may be addressed working on the solution equilibria. Several M-Rh species (M = Fe, Ru, Os, Ir, Pt) have been specifically synthesized yielding the MRh 4, and MRh 5 families of homologous compounds where rhodium prevails as the main component of the metal skeleton. As a consequence the main structural and physical properties of these species are always strictly related to those of the corresponding homometallic rhodium species. On the other hand, the presence of the M heterometal acts as a ‘fine tuner’ giving to any member of these families specific properties, such as the reactivity and the NMR chemical shifts.

Optimizing myocardial hypothermia: II. Cooling jacket modifications and clinical results

After induction of myocardial hypothermia by cold cardioplegic solution, myocardial rewarming occurs at 0.5 ° to 1.0 °C/min. In addition to preventing myocardial rewarming from systemic and pulmonary venous return, continuous cooling of the myocardial surface must be provided. Modifications of a previously reported cooling jacket are described. These modifications include decreased width and thickness of the metal skeleton for easier application and increased malleability, respectively. Also, the double-row flow channel markedly minimizes obstruction of flow secondary to kinking and allows inlet and outlet lines to attach at adjacent points of the jacket thus minimizing obstruction of the operative field. The effectiveness of the jacket in 36 patients undergoing valve replacement and 19 patients having pulmonary thromboendarterectomy was evaluated by measurement of myocardial temperatures at multiple sites throughout aortic cross-clamping. Temperatures at all sites were maintained at 12 °C or less. Temperatures measured in phrenic nerve pedicles ranged from 25 ° to 27 °C. During cooling, heat removal by the jacket was 330 calories/min. During maintenance of myocardial hypothermia, heat flow was 190 calories/min. Modifications of a cooling jacket facilitate usability and an array of sizes enhances applicability.

Synthesis and crystal structure of [Ru3Pt(µ-PPh2)(µ4-η2-CCBut)(CO)7(dppe)](dppe = Ph2PCH2CH2PPh2), a butterfly cluster containing an unusually bonded alkynyl ligand: a model for an intermediate molecular geometry in a cluster-ligand rearrangement

Reaction of [Ru3Pt(µ-H)(µ4-η2-CCBut)(CO)9(L2)]la(L2= dppe) with Ph2PCCPPh2 affords the butterfly cluster [Ru3Pt(µ-PPh2)(µ4-η2-CCBut)(CO)7(dppe)]3; the metal skeleton and µ4-η2 alkynyl coordination mode in 3 represent a likely model for a transition geometry in the interconversion of 1 and its vinylidene tautomer [Ru3Pt{µ4-η2-CC(H)But}(CO)9(L2)]2.

Giant palladium clusters: synthesis and characterization

A series of palladium clusters containing from four to several hundred Pd atoms in the metal skeleton has been prepared and characterized with respect to structure and chemical properties, including catalytic activity. For smaller clusters good agreement was observed. between single-crystal X-ray and EXAFS structural data. Giant clusters approximating to Pd561L60(OCOCH3)180(L = phen, bipy) and Pd561phen60O60X60(X = PF6, ClO4, BF4, CF3CO2), were characterized with TEM, SAXS, EXAFS, NMR and magnetic succeptibility data. These clusters contain a closepacked metal core and ligands L and X that are located at the periphery of a cluster. They are very soluble in water and polar organic solvents and can be considered as a bridge between low molecular clusters and particles of colloidal metals. Giant Pd clusters were found to be active homogeneous catalysts for various organic reactions, e.g. oxidative acetoxylation of alkenes and alkylarenes; oxidation of alkenes, formic acid and alcohols; dehydration of alcohols and formation of acetals. The kinetics and mechanism of the homogeneous oxidation of alkenes and HCO2H in solutions of giant clusters were elucidated.

The heteronuclear cluster chemistry of the Group IB metals XIV. The influence of the P(CH 2Ph) 3 ligand on the metal framework structures adopted by mixed-metal clusters containing M{P(CH 2Ph) 3} (M  Cu or Ag) fragments. Crystal structures of [Cu 2Ru 4(μ 3-H) 2(CO) 12{μ-P(CH 2Ph) 2-(η 2-CH 2Ph)}] and [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2

Treatment of a dichloromethane solution of the salt [N(PPh 3) 2] 2[Ru 4(μ-H) 2(CO) 12] with two equivalents of the complex [M(NCMe) 4]PF 6 (M  Cu or Ag) at −30°C, followed by the addition of two equivalents of P(CH 2Ph) 3, affords the novel mixed-metal cluster compound [Cu 2Ru 4(μ 3-H) 2(CO) 12{μ-P(CH 2Ph) 2(η 2-CH 2Ph)}] (77% yield) when M  Cu, whereas the expected product, [Ag 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] (37% yield), is obtained for M  Ag. When an acetone solution of [N(PPh 3) 2] 2[Ru 4(μ-H) 2(CO) 12] is treated with a dichloromethane solution containing two equivalents of the compound [CuCl{P(CH 2Ph) 3}], in the presence of TlPF 6, a mixture of [Cu 2Ru 4(μ 3-H) 2(CO) 12{μ-P(CH 2Ph) 2(η 2-CH 2Ph)}] (44% yield) and [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] (12% yield) is produced. Single-crystal X-ray diffraction studies were performed on [Cu 2Ru 4(μ 3-H) 2(CO) 12 {μ-P(CH 2Ph) 2(η 2-CH 2Ph)}] and [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2]. The former cluster exhibits a capped trigonal bipyramidal metal framework structure (CuCu 2.532(2), CuRu 2.585(2)–2.813(1), RuRu 2.790(1)–2.981(1) Å) and the single P(CH 2Ph) 3 group adopts a novel bidentate bonding mode by bridging the two adjacent copper atoms via bonds from its phosphorus atom (CuP 2.199(2) Å) and an η 2-CH 2Ph ring (CuC 2.146(10) and 2.339(12) Å). In marked contrast, [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] adopts an unusual metal core structure, which consists of a Ru 4 tetrahedron with one edge bridged by a Cu{P(CH 2Ph) 3} unit and a non-adjacent face capped by the second Cu{P(CH 2Ph) 3} group (CuRu 2.589(4)–2.724(4), RuRu 2.760(3)–2.984(4) Å). Infrared and NMR spectroscopic data show that [Ag 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2] exhibits a capped trigonal bipyramidal skeletal geometry, with the silver atoms in close contact. Thus, although the P(CH 2Ph) 3 ligand is evidently too bulky to allow two adjacent Cu{P(CH 2Ph) 3} units to be accommodated in the metal skeleton of [Cu 2Ru 4(μ 3-H) 2(CO) 12{P(CH 2Ph) 3} 2], the greater size of the silver atom relative to copper means that the analogous silver-containing species can adopt the metal framework structure which previous work suggests is preferred by clusters of this type. Variable-temperature 31P-{ 1H} and 1H NMR spectroscopic studies demonstrate that all three of the new heteronuclear cluster compounds undergo a number of interesting dynamic processes in solution.

Glass Space Structures

This article describes the development of several methods of structural use of glass panels in spatial structures, ranging from non-loadbearing glass panels in conventional skylights around space frames, via structurally sealed glass panels also having an extra stabilising function for the metal skeleton, to structurally load-bearing glass panels, where metal elements are only used as connection elements for additional stability. The point of view of the author is that of a product-architect, who combines the profession of an architect, a structural engineer, an industrial designer on the one hand, and a manufacturer/specialist-contractor for spatial structures plus claddings in architecture on the other hand.

ChemInform Abstract: Tetranuclear Carbonyls of Osmium

Abstract Osmium forms more neutral binary carbonyls than any other metal; before 1987, nine were known with one to eight osmium atoms. There were, however, no tetranuclear binary carbonyls of osmium known before this data. This review describes the synthesis of Os4(CO)14 (1), Os4(CO)15 (2) and Os4(CO)16 (3) along with various derivatives of these clusters. Addition of Os(CO)5 to Os3(CO)10(C8H14)2 in hexane affords 2 in good yield. The crystal structure of 2 reveals it to have an unusual planar structure with short (2.775 A) and long (2.998 A) peripheral Os—Os bonds (the hinge Os—Os bond length of 2.948 A is more typical of an Os—Os single bond). The unusual metal—metal bond lengths are rationalized in terms of three-center, two-electron metal—metal bonds so that the short bonds have a bond order of 1.5 and the long bonds an order of 0.5. In this way each osmium atom achieves an 18-electron configuration. Several clusters with essentially the same arrangement of metal atoms have also been synthesized (e.g., Os4(CO)14(PMe3) (4), (η5- C5Me5)IrOs3(CO)12). The variable temperature 13C NMR spectra of 2 and 4 indicate that rapid CO-exchange in the equatorial plane occurs in these compounds. Other 62-electron clusters prepared in this study were Os4(μ-H)(CO)14(SnMe3) (8) and Os4(μ-H)2(CO)13(PMe3) (9); whereas 8 has a planar metal skeleton, 9 adopts the more common butterfly arrangement. For these clusters, the planar configuration is adopted when at least one of the metal atoms in the hinge position has four terminal ligands. Refluxing 2 in hexane yields Os4(CO)14 (1), which as expected from polyhedral skeletal electron pair theory has a tetrahedral metal core. Evidence is presented which indicates that in solution the carbonyl ligands in 1 undergo exchange on the infrared time scale. Treatment of 2 in CH2Cl2 at 0 ° C with CO (1 atm) gives Os4(CO)16 (3) in essentially quantitative yield. The crystal structure of 3 reveals it to have a cyclobutane-like Os4 core; the Os—Os bonds are long and range in length from 2.979 to 3.000 A. In solution at room temperature, 3 readily decomposes to give mainly Os3(CO)12. The much greater stability of the trinuclear cluster suggests that the metal—metal bonding in this cluster should be described in terms of a centrally directed molecular orbital plus edge-bridging molecular orbitals, rather than in terms of two-center, two-electron metal—metal bonds. The structures of Os4(CO)15(L) (L = PF3, PMe3, P(OCH2)3CMe, CNBut) have been determined. Only the PF3 derivative has a puckered square arrangement of metal atoms (with long Os—Os bonds) like 3; the other derivatives have a spiked triangular arrangement of metal atoms. The Os—Os bond lengths in the latter clusters range from 2.849 to 2.938 A. From this study it is concluded that it is the electronic properties of L that dictate which structure a cluster of the type Os4(CO)15(L) adopts. The nonrigid properties of 3 and the Os4(CO)15(L) clusters are also briefly discussed. t001 . The neutral binary carbonyls of osmium known before 1987 Formula Structure Ref. Os(CO)5 trigonal bipyramidal (D3h) 1 Os2(CO)9 single carbonyl bridge (C2v) a 2 Os3(CO)12 triangular Os3 (D3h) 3 Os5(CO)16 trigonal bipyramidal Os5 4 Os5(CO)19 “bow-tie” Os5 5 Os6(CO)18 capped trigonal bipyramidal Os6 6 Os6(CO)21 planar, “raft-like” Os6 b 7 Os7(CO)21 capped octahedral Os7 9 Os8(CO)23 bicapped octahedral Os8 c a Probable structure. b Probable structure based on the structures of Os6(CO)21-x[P(OMe)3]x (x = 1−4) [18,81]. c B.F.G. Johnson, personal communication.

Tetranuclear carbonyls of osmium

Osmium forms more neutral binary carbonyls than any other metal; before 1987, nine were known with one to eight osmium atoms. There were, however, no tetranuclear binary carbonyls of osmium known before this data. This review describes the synthesis of Os 4(CO) 14 ( 1), Os 4(CO) 15 ( 2) and Os 4(CO) 16 ( 3) along with various derivatives of these clusters. Addition of Os(CO) 5 to Os 3(CO) 10(C 8H 14) 2 in hexane affords 2 in good yield. The crystal structure of 2 reveals it to have an unusual planar structure with short (2.775 Å) and long (2.998 Å) peripheral Os—Os bonds (the hinge Os—Os bond length of 2.948 Å is more typical of an Os—Os single bond). The unusual metal—metal bond lengths are rationalized in terms of three-center, two-electron metal—metal bonds so that the short bonds have a bond order of 1.5 and the long bonds an order of 0.5. In this way each osmium atom achieves an 18-electron configuration. Several clusters with essentially the same arrangement of metal atoms have also been synthesized (e.g., Os 4(CO) 14(PMe 3) ( 4), (η 5- C 5Me 5)IrOs 3(CO) 12). The variable temperature 13C NMR spectra of 2 and 4 indicate that rapid CO-exchange in the equatorial plane occurs in these compounds. Other 62-electron clusters prepared in this study were Os 4(μ-H)(CO) 14(SnMe 3) ( 8) and Os 4(μ-H) 2(CO) 13(PMe 3) ( 9); whereas 8 has a planar metal skeleton, 9 adopts the more common butterfly arrangement. For these clusters, the planar configuration is adopted when at least one of the metal atoms in the hinge position has four terminal ligands. Refluxing 2 in hexane yields Os 4(CO) 14 ( 1), which as expected from polyhedral skeletal electron pair theory has a tetrahedral metal core. Evidence is presented which indicates that in solution the carbonyl ligands in 1 undergo exchange on the infrared time scale. Treatment of 2 in CH 2Cl 2 at 0 ° C with CO (1 atm) gives Os 4(CO) 16 ( 3) in essentially quantitative yield. The crystal structure of 3 reveals it to have a cyclobutane-like Os 4 core; the Os—Os bonds are long and range in length from 2.979 to 3.000 Å. In solution at room temperature, 3 readily decomposes to give mainly Os 3(CO) 12. The much greater stability of the trinuclear cluster suggests that the metal—metal bonding in this cluster should be described in terms of a centrally directed molecular orbital plus edge-bridging molecular orbitals, rather than in terms of two-center, two-electron metal—metal bonds. The structures of Os 4(CO) 15(L) (L = PF 3, PMe 3, P(OCH 2) 3CMe, CNBu t) have been determined. Only the PF 3 derivative has a puckered square arrangement of metal atoms (with long Os—Os bonds) like 3; the other derivatives have a spiked triangular arrangement of metal atoms. The Os—Os bond lengths in the latter clusters range from 2.849 to 2.938 Å. From this study it is concluded that it is the electronic properties of L that dictate which structure a cluster of the type Os 4(CO) 15(L) adopts. The nonrigid properties of 3 and the Os 4(CO) 15(L) clusters are also briefly discussed. t001 The neutral binary carbonyls of osmium known before 1987 Formula Structure Ref. Os(CO) 5 trigonal bipyramidal ( D 3 h ) 1 Os 2(CO) 9 single carbonyl bridge ( C 2 v ) a 2 Os 3(CO) 12 triangular Os 3 ( D 3 h ) 3 Os 5(CO) 16 trigonal bipyramidal Os 5 4 Os 5(CO) 19 “bow-tie” Os 5 5 Os 6(CO) 18 capped trigonal bipyramidal Os 6 6 Os 6(CO) 21 planar, “raft-like” Os 6 b 7 Os 7(CO) 21 capped octahedral Os 7 9 Os 8(CO) 23 bicapped octahedral Os 8 c a Probable structure. b Probable structure based on the structures of Os 6(CO) 21- x [P(OMe) 3] x ( x = 1−4) [18,81]. c B.F.G. Johnson, personal communication.

Giant palladium clusters as catalysts of oxidative reactions of olefins and alcohols

Giant cationic palladium clusters approximated as Pd 561L 60(OAc) 180 (L = phen, bipy) and Pd 561phen 60O 60(PF 6) 60 were synthesized and characterized with high resolution TEM, SAXS, EXAFS, IR and magnetic susceptibility data. The results of these studies suggest that L and O ligands are bound to Pd atoms located on the surfaces of close-packed metal skeletons of the clusters, while OAc −1 and PF 6 − anions are outer-sphere ligands. Under mild conditions (293–363 K, l atm) the giant palladium clusters catalyze oxidative acetoxylation of ethylene into vinyl acetate, propylene into allyl acetate, and toluene into benzyl acetate; oxidation of primary aliphatic alcohols into esters; and conversion of aldehydes into acetals. Kinetics of oxidative acetoxylation of ethylene and propylene in solutions of the giant clusters were studied. A mechanism for these reactions is proposed, which includes the following steps: coordination of reagents by the cluster, oxidative addition of alkene to a Pd—Pd fragment and transfer of an electron pair from a Pd—H, Pd—vinyl, or Pd—allyl fragment to a coordinated molecule of oxidant (O 2, peroxide, Pd(II)).

A role of non-bonding interactions in the chemistry of organometalic compounds

The degree of space shielding of skeleton metal atoms by ligands (radicals) in molecules of organometallic compounds, comprising metal atom chains or plane metal cycles, is calculated. The calculations involved constructing the projection of the molecule onto the closed, continuous surface embracing metal skeleton, as well as calculation of the total ( S) and shielded area ( S s) squares of this surface. The ratio K= S s/ S was taken as a shielding degree. A role of non-bonding interactions in the formation of the molecule structure and the structure of a condensed state of organometallic compounds are discussed.